Heated dilution method for a liquid sample

ABSTRACT

An analyzer system for improving quality of a reaction product, wherein a liquid sample must be maintained at an elevated temperature to prevent precipitation of titratable species, comprises a heated sample and dilution section, an autotitrator and a programmable controller. In operation a liquid sample to be analyzed is withdrawn from a reactor and maintained at reactor temperature while being diluted. The diluted sample is then cooled and passed to an autotitrator for analysis. The analyzer system includes a programmable controller for automatic unattended dilution of successive samples.

This application is a continuation of application Ser. No. 617,321,filed Nov. 23, 1990 now abandoned.

This invention relates to chemical analysis of a diluted sample. In oneaspect this invention relates to method and apparatus for obtaining anddiluting samples of solutions which must be maintained at an elevatedtemperature to prevent precipitation of titratable species. In anotheraspect this invention relates to method and apparatus for analysis of amaterial by titration.

BACKGROUND OF INVENTION

As used herein, a pH titration involves the incremental addition of astandard acid to a carefully measured quantity of aqueous solutionduring which pH values and the aliquots of reagent added are recorded. Atitration curve si a plot of these data. The titration curve isinvaluable in determining the equivalence point in a pH titration. Oneproblem encountered in the analysis of certain materials is that ofpreparing a diluted sample of the material, when the material to beanalyzed must be dissolved at elevated temperatures. For example,titration analysis can be valuable in determining the mole percent ratioof titratable species in a process for preparing sodium sulfidesolutions by reacting sodium hydroxide with sodium hydrosulfide,provided the reaction material can be dissolved in a solution fortitration analysis.

Accordingly, it is an object of this invention to provide method andapparatus suitable for titration analysis of materials which dissolveonly at elevated temperature.

Another object of this invention is to provide an apparatus and methodfor diluting a highly viscous and corrosive sample material.

Still another object of this invention is to provide an apparatus forsample handling with heating and cooling.

Yet another object of this invention is to provide an apparatus andmethod for automatic, unattended dilution of a highly viscous andcorrosive sample material.

SUMMARY OF THE INVENTION

In accordance with the present invention an apparatus and a method aredisclosed wherein a liquid sample of material to be analyzed iswithdrawn from a reactor at reactor temperature and flows under reactorpressure through a sample conduit having a predetermined volume. Fromthe sample conduit the liquid sample flows into a first cylinder whichis sealed off from other external pressure, and which has a volumegreater than the sample conduit. Since flow of sample material from thereactor is a result of reactor pressure and the liquid sample materialis allowed to accumulate in the first cylinder, the flow stops when thepressure in the first cylinder substantially equals the reactorpressure. Pressure transferring the sample material in this mannerassures that the sample conduit is full of material when flow from thereactor stops. The thus obtained measured quantity of sample materialcontained in the sample conduit is diluted by mixing with a liquiddiluent contained in a second cylinder, with the second cylinder havinga predetermined volume relationship with the sample conduit, so as toprovide a diluted sample of material suitable for analysis by titration.

In a preferred embodiment, the sample conduit, the first and secondcylinders and valve means for selectively establishing fluidcommunication between the reactor, sample conduit, first cylinder andsecond cylinder, are located in a heated enclosure which is maintainedat a temperature substantially equal to the temperature of the samplematerial withdrawn from the reactor. After dilution int eh heatedenclosure, the diluted sample is cooled in a heat exchanger and passedto an autotitrator for automatic titration analysis. Further inaccordance with a preferred embodiment, the sample material is obtainedand diluted under a programmed sequence of valve operations generated bya suitable programmable controller. In this latter preferred embodiment,automatic unattended dilution of successive samples is achieved byemploying control valves which can be remotely operated by signalsgenerated in the programmable controller.

Other objects and advantages of the invention will be apparent from theforegoing brief description of the invention and the appended claims aswell as the detailed description of the drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic representation of a liquid dilution systemtogether with apparatus for obtaining a sample of a material accordingto the invention.

FIG. 2 is a block diagram of an analyzer system incorporating the liquiddilution system illustrated in FIG. 1.

FIG. 3 is a flow diagram for programming a programmable controller,which illustrates the sequence of valve operation for obtaining anddiluting a sample of material.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention is descried in terms of a particular configuration of ananalyzer system and in terms of a particular sampling and dilutingapparatus configuration. The invention is applicable, however, to anyapparatus configuration which accomplishes the purpose of the invention.The invention is also described in terms of sampling a sodium sulfidereactor but is generally applicable to liquid samples which must bediluted at an elevated temperature.

The pairs of 3-way diverting valves such as 22 and 24, as well as otherpairs of 3-way valves illustrated in FIG. 1, are ganged together tooperate simultaneously as indicated by the dashed lines 26, 40 and 42.Also on all of the 3-way valves illustrated in FIG. 1, the solid blackport indicates the blocked port for diverting liquid in the valves, whenthe valve is in tis normal or unactivated state. In the active state ofthe 3-way valves illustrated in FIG. 1, the port opposite the solidblack pot is blocked.

Referring now to FIG. 1, a sample of liquid reaction product iswithdrawn from reactor 10 under reaction conditions. A point is selectedon the reactor for installing a sample take-off port 13 to obtain arepresentative sample of reaction product, and the liquid sample isforced by reactor pressure to flow from reactor 10 through steam heatedconduit 12 into the heated enclosure 14. In the enclosure 14 the samplematerial flows through an arrangement of valves and conduits, as will bemore fully described hereinafter, the accumulates in holding cylinder 30which is sealed off from other externally applied pressure. Cylinder 30is preferably teflon lined for holding corrosive material.

Flow of sample material form the reactor 10 to the closed cylinder 30continues until the pressure in cylinder 30 substantially equalizes withthe pressure in reactor 10. Since the sample material flows through thesample conduit 16 prior to entering the cylinder 30, there is assurancethat the sample conduit 16 is completely full of sample material whenflow from the reactor stops.

The liquid stream flowing in conduit 12 is provided to one end of thesample conduit 16 via block valve 18, conduit 20, and 3-way valve 22.The sample conduit 16, which extends between 3-way valves 22 and 24, hasa predetermined volume, for example, a volume of about 18 mL. the volumeof about 18 mL for the sample conduit is suitable for sampling reactionmaterial from a sodium sulfide reactor for analysis by an autotitrator.From the sample conduit 16 the sample liquid flows through 3-way valve24 and conduit 28, into a holding cylinder 30 when a liquid sample isbeing withdrawn from the reactor 10. When the liquid sample s beingdiluted, however, the liquid flowing from sample conduit 16 is divertedby 3-way valve 24 to flow through the combination of conduit 32, 3-wayvalve 34 and conduit 36 into mixing cylinder 38. For diluting an 18 mLsample of sodium sulfide solution, the volume of cylinders 38 can beabout 1 liter.

From the cylinder 30 sample liquid may be returned to the reactor 10 viathe sample loop 16 and the combination of valves 18, 22 and 24 understeam pressure, which is supplied form an external source via valve 44and the combination of conduits 46 and 48. The external steam sourcealso supplies heat to conduit 12 via conduit 46.

From cylinder 38, which initially contains a predetermined volume of asuitable liquid diluent, liquid may be withdrawn for diluting the samplematerial in sample conduit 16. The diluent liquid is directed to flow ina closed loop pathway which includes sample conduit 16. The closedpathway is via conduit 50, 56, 60, 62, 66, 16, 32 and 36, which includes3-way valves 54, 58, 64, 22, 24 and 34, and also pump 52. Circulation ofthe measured quantity of sample material from sample conduit 16 and themeasured quantity of liquid diluent from cylinder 38 is continued untila substantially uniform mixture thereof is obtained. Any suitable lengthof mixing time and flow rate in the closed loop pathway may be utilized.The exact time required for each specific apparatus configuration beingdependent upon the relative volume of the closed loop pathway, the speedand capacity of the pump 52, the solubility and mobility of the samplematerial in the diluent liquid, the turbulence of flow through theclosed loop pathway and other similar parameters. For a sample materialof 18 mL of sodium sulfide solution which is combined with 1 liter ofhot distilled water in cylinder 38, a flow rate in the closed pathway ofabout 1 liter per minute for a time period of about 5 minutes has beenfound to be satisfactory.

Air pressure supplied via conduit 68 may be used to force the uniformlydiluted sample material form the enclosure 14 through conduit 70. Theuniformly diluted sample, which is representative of the reactionmaterial, is cooled in heat exchanger 72 and transported to an analyzerinstrument such as a titrator, or for other use of the diluted samplematerial, via conduit 70.

Cylinder 38 can be refilled with diluent from supply cylinder 74 viaconduits 76 and 50, and valve 54. To insure complete filling of cylinder38, it may be filled to overflow so as to cause a flow to drain viavalve 34 and conduit 78. Cylinder 74, which is preferably about 3 timesas large as cylinder 38, is maintained full of diluent liquid to providea preheated supply of diluent liquid. The diluent liquid may be suppliedunder pressure to cylinder 74 from an external source via conduit 78 tomaintain cylinder 74 full of liquid.

The enclosure 14 will preferably be maintained at a temperaturesubstantially equal to the temperature o the reaction material inreactor 10. The temperature of the reaction material will typically be260° F. or greater. The invention is applicable, however, to higher orlower temperatures, depending on the temperature required to maintainthe sample material in a soluble state for dilution and analysis bytitration after dilution.

Temperature control of the enclosure 14 is accomplished by means of theair heater 73. Air is supplied to the air heater 73 via conduit 71 andthe heater 73 is controlled in a conventional manner to maintain adesired temperature in enclosure 14.

Referring now to FIG. 2, where like reference numerals are used for theparts which are also illustrated in FIG. 1, there is illustrated a blockdiagram of an analyzer system for analyzing a diluted sample obtainedfrom the reactor 10. The analyzer system includes the heated dilutionsystem in enclosure 14, a programmable controller (PC) 80 having a valveactuator section and printer/keyboard 90, and an autotitrator 82. Thisanalyzer system enhances reactor product quality by insuring moreuniform reaction products. Any suitable autotitrator may be utilized inthe practice of this invention, an example of an autotitrator is anIONICS 3000 AUTOTITRATOR.

The PC 80 orchestrates operation of the sample dilution 14 and theautotitrator 82 by providing suitable signals via lines 84 and 86respectively. The signal line 84 represents a plurality of signals whichare provided so as to properly sequence the valves illustrated inFIG. 1. The valve actuator section of the PC 80 is a preferred means forsupplying pneumatic pressure signals to pneumatic actuators, which canbe associated with valves 18, 22, 24, 34, 44, 47, 54, 58 and 64illustrated in FIG. 1 for remotely operating these valves. Theinvention, however, is also applicable to electrical, mechanical,hydraulic or other signal transmitting means. The PC 80 also provides astart analysis signal 86 to the autotitrator 82 and receives anautotitrator ready signal 88 from the autotitrator 82. Any suitable PChaving the capability of remotely operating control valves in aprogrammed sequence can be used in the practice of this invention.Suitable programmable controllers and control valves are described atlength in chapter 6.4 of Liptak, B. G. "Instrument Engineer Handbook"Process Control, Chilton Book Co., 1985.

Referring now to FIG. 3, the sequence requirement for opening andclosing valves 18, 22, 24, 34, 4, 47, 54, 58 and 64, which are shown inFIG. 1, is illustrated by a flow diagram. In the flow diagram all 2-wayvalves are assumed to be initially closed and all 3-way valves areinitially in their normal (unactuated) position as shown in FIG. 1.

The first step in the sample dilution sequence flushes the cylinder 30and the sample conduit 16 with steam, with the steam and any othermaterial flushed from the cylinder or conduit being passed into thereactor 10. This step returns any residual sample material in cylinder30 or sample conduit 16 back into the reactor 10. The delay associatedwith this step, and with other delays associated with all of thesubsequent steps, will depend upon a number of factors such as thevolume of the cylinders, the steam pressure utilized, the solubility andmobility of the sample material being analyzed, the valve and conduitsizes utilized, and other similar parameters. The time required for anyof these steps in a particular operation will generally be obvious to aperson skilled in the art. For example, in a prototype operationaccording to this invention, which utilized 1/4" conduits for handlingsodium sulfide solution, 1 liter cylinders, 40 psig steam, etc., a flushtime of 2 minutes was found to be satisfactory.

Step 2 begins withdrawal of the sample material from the reactor 10while cylinder 30 is being vented through valve 47 for ten seconds aftersample material withdrawal begins. Sample withdrawal continues until thepressure in cylinder 30 equalizes with the pressure in reactor 10.During this time cylinder 30 is at least partially filled with samplematerial and sample conduit 16 is completely filled with sample materialwhile cylinder 38 is completely refilled with diluent liquid.

Step 3 prevents flow of sample material form the reactor 10 at a timethat insures the sample conduit 16 is filled with sample material, andfurther isolates the sample conduit 16 from the cylinder 30 whileconnecting the sample conduit and cylinder 38 in a closed loop viavalves 54, 58, 64, 22, 24 and 34. Step 3 also causes mixing of themeasured quantity of sample material in sample conduit 16 with themeasured quantity of diluent liquid in cylinder 38 for a time periodnecessary to obtain a uniform mixture.

Step 4 transports the diluted sample material to the autotitrator 82,and the PC 80 issues a start signal to the autotitrator.

Step 5 flushes the cylinder 30 and the sample conduit 16 with steam intoreactor 10 and fills cylinder 38 with diluent liquid.

Step 6 circulates the diluent liquid contained in cylinder 38 through aclosed path, which includes sample conduit 16 and the cylinder 38, so asto wash these components. For the above mentioned prototype system,using distilled water as the diluent liquid, a wash period of fourminutes was utilized. Step 6 concludes by draining this wash liquid viaconduit 70 through a drain in the autotitrator 82.

Step 7 repeats the wash cycle by first filling cylinder 38 with diluentliquid and then circulating the liquid through a closed path, whichincludes sample conduit 16 and the cylinder 38. The wash liquid isdrained via conduit 70 as in Step 6.

Step 8 requires the PC 80 to wait before starting the nextsampling-analysis sequence. On completion of the analysis, theautotitrator 82 returns a ready signal to the PC and thesampling-analysis sequence starts again at Step 1.

The following example illustrates analysis of sample material withdrawnfrom a sodium sulfide reactor wherein the sample contains a minor amountof sodium hydrosulfide. This example is intended to further assist oneskilled in the art to an understanding of this invention and is notlimitable of the reasonable scope of this invention.

EXAMPLE I

This example shows that the inventive sampling, dilution and titrationtechnique, which was carried out in conjunction with a pilot plantreactor, gave values for titratable species which corresponded favorablyin magnitude to the values for these species calculated for combinedportions of more concentrated stock solutions. For purposes of thisexample, commercially available solutions containing a major amount ofsodium sulfide (Na₂ S) and a minor amount of sodium hydrosulfide (NaSH)were prepared by mixing the necessary quantities of a commerciallyavailable sodium hydroxide solution (NaOH) and a commercially availablesodium hydrosulfide solution (NaSH). The minor amount of sodiumhydrosulfide (NaSH) desired in the system was about 3 mole % based onthe total amount of Na₂ S in the mixture.

The following equation (i) describes the reaction which takes place onmixing the commercially available solutions of NaOH and NaSH:

    NaOH+NaSH→Na.sub.2 S+H.sub.2 O                      (i)

According to the stoichiometry, one mole of NaOH reacts with one mole ofNaSH to give one mole of Na₂ S and one mole of H₂ O. Since it wasdesired to prepare concentrated solutions of Na₂ S containing about 3mole % of NaSH based on total Na₂ S, the amount of NaSH added wasappropriately adjusted to the desired stoichiometric excess over NaOH.Table I summarizes the amounts used in designated samples, I, II, IIIand IV.

                  TABLE I                                                         ______________________________________                                        Concentrated Stock Solutions of Na.sub.2 S Prepared From                      Commercially Available Solutions of NaOH.sup.a and NaSH.sup.b                                                 Approximate                                           lb Commercial                                                                             lb Commercial                                                                             Molar                                         Reference                                                                             NaOH Solution                                                                             NaSH Solution                                                                             % Excess NaSH.sup.c                           ______________________________________                                        Sample I                                                                              76.0        88.3.sup.e  3.5                                           Sample II                                                                             76.1        88.2.sup.f  3.2                                           Sample III                                                                            76.0        88.2        3.3                                           Sample IV                                                                             76.1        88.3        3.3                                           ______________________________________                                         .sup.a The commercial aqueous sodium hydroxide solution was about 47.1        weight percent NaOH.                                                          .sup.b The commercial aqueous sodium hydrosulfide solution was about 58.8     weight percent NaSH and contained about 0.3 weight percent sodium sulfide     (Na.sub.2 S).                                                                 .sup.c Takes into account the 0.003 lb mole Na.sub.2 S added in the NaSH      solution.                                                                     .sup.d The 76.0 lb portions of NaOH solution contained 0.895 lb mole of       NaOH and the 76.1 lb portions contained 0.896 lb mole of NaOH.                .sup.e,f The 88.2 and 88.3 lb portions of the NaSH solution contained,        respectively, 0.925 and 0.926 lb mole of NaSH.                           

From the facts given in Table I, it is apparent that the originalmixtures which were diluted, sampled and titrated in accordance with theinventive procedure contained titratable species Na₂ S and NaSH.

The following equations (ii) and (iii) describe the step-wise reactionswhich occur in the HCl titration of the diluted Na₂ S solution:

    Na.sub.2 S+HCl→NaSH+NaCl                            (ii)

    NaSH+HCl→H.sub.2 S+NaCl                             (iii)

The "first endpoint" corresponds to that point at which sufficient HClhas been added to convert all the Na₂ S to NaSH and NaCl. The "secondendpoint" corresponds to that point at which sufficient HCl has beenadded to convert all the NaSH to H₂ S and NaCl. According to thestoichiometry, the amount of HCl theoretically required to reach the"first endpoint" would be the same as that required to reach the "secondendpoint" if Na₂ S were the only titratable specie in the originalmixture.

Equation (ii), e.g., indicates that one mole of Na₂ S reacts with onemole of HCl to give one mole of NaSH and one mole of NaCl. Equation(iii), e.g., indicates that one mole of NaSH reacts with one mole of HClto give one mole of H₂ S and one mole of NaCl.

In the instant operation, the desired stock solution was prepared tohave about a 3 molar % concentration of NaSH in the original Na₂ Ssolution based on the concentration of sodium sulfide (see Table I).Titration of these systems, designated as samples I, II III and IV,would thus require more HCl to reach the "second endpoint" than wasrequired to reach the "first endpoint". This follows from the fact thatthe second phase of the titration involves the reaction of the NaSHproduced in equation (ii) with HCl as well as reaction of the additionalNaSH reagent deliberately added to the original Na₂ S solutionpreparation. This difference in the amounts of HCl required,respectively, to reach the "first endpoint" and "second endpoint"corresponds to the excess of NaSH provided in the preparation of theoriginal Na₂ S solutions.

Titrations of the samples I, II, III and IV summarized in Table II werecarried out to determine the molar % excess of NaSH in each of thesystems.

                                      TABLE II                                    __________________________________________________________________________    Titrations of Na.sub.2 S Solutions Prepared from Commercially                 Available NaOH.sup.a and NaSH.sup.b Solutions                                     Column 1                                                                             Column 2                                                                             Column 3 Column 4                                                                             Column 5                                        mmoles HCl                                                                           mmoles HCl                                                                           Excess mmoles                                                                          % Molar                                                                              % Molar                                         to     to     HCl.sup.e                                                                              Excess NaSH                                                                          Excess NaSH                                 Sample                                                                            EP-1.sup.c                                                                           EP-2.sup.d                                                                           (EP-2) - (EP-1)                                                                        (Titration).sup.g                                                                    (Table I)                                   __________________________________________________________________________    I   0.449  0.465  0.016    3.6    3.5                                         II  0.469  0.482  0.013    2.8    3.2                                         III.sup.f                                                                         0.531  0.546  0.015    2.8    3.3                                         IV  0.464  0.478  0.014    3.0    3.3                                         __________________________________________________________________________     .sup.a See footnote a in Table I.                                             .sup.b See footnote b in Table I.                                             .sup.c EP-1 represents first endpoint: the mmoles HCl values cited in I,      II and IV are the averages of 3 titration runs.                               .sup.d EP-2 represents second endpoint: the mmoles HCl values cited in I,     II and IV are the averages of 3 titration runs.                               .sup.e Values also correspond numerically to excess mmoles of NaSH in the     system.                                                                       .sup.f The mmoles HCl values are the averages of 5 titration runs.            .sup.g The values in column 4 were calculated by dividing the values in       column 3 by the values in column 1 and multiplying the quotient by 100.  

Referring to the results in Table II, it can be seen that the molar %excess value for NaSH determined by the inventive sampling, dilution andtitration technique agreed favorably with the analogous values based onthe weighed quantities of commercial solutions of NaOH and NaSH whichwere mixed to give the original unreacted Na₂ S/NaSH solutions.

That which is claimed is:
 1. A method of obtaining a sample of areaction solution containing a material which dissolves only at anelevated temperature and diluting said sample for chemical titrametricanalysis, said method comprising:a) venting a first vessel toatmospheric pressure; b) after step a), establishing flow of saidreaction solution to be analyzed from an elevated pressure in a reactorand directing low of said reaction solution through a sample conduithaving a pre-determined volume, and then into said first vessel whilemaintaining said reaction solution at said elevated temperature; c)after step b), sealing off said first vessel from atmospheric pressure;d) allowing flow of said reaction solution to accumulate in said firstvessel until the pressure in said first vessel substantially equals thepressure in said reactor, thereby assuring that said sample conduit isfull of said reaction solution when flow stops, wherein the volume ofreaction solution in said sample conduit provides said sample ofreaction solution; e) diluting said sample of reaction solution at saidelevated temperature by mixing with a predetermined volume of liquiddiluent contained in a second vessel to provide a diluted sample; f)passing said diluted sample to a titrametric analyzer; and g)backflushing reaction solution in said first vessel and said sampleconduit to said reactor.
 2. A method in accordance with claim 1, whereinsaid sample conduit is connected between corresponding first ports oneach of a first pair of three-way valves and said first vessel isconnected to a second port on one of said first pair of three-wayvalves, said first pair of three-way valves having first and secondpositions, wherein said reactor includes a sample take-off port, andwherein said step for directing flow of reaction solutioncomprises:flowing said reaction solution from said sample take-off portthrough a heated conduit having a block valve located therein and thento the second port on the other one of said first pair of three-wayvalves; and placing said first pair of three-way valves in said secondposition, whereby fluid communication is established between saidreactor and said first vessel.
 3. A method in accordance with claim 2,wherein said second vessel is connected between corresponding firstports on a second pair of three-way valves and a pump is connectedbetween corresponding first ports on a third pair of three-way valves,said second and third pair of three-way valves having first and secondpositions, wherein said step of diluting said sample comprises:placingeach of said first, second and third paris of three-way valves in aidfirst position so as to interconnect said sample conduit, said secondvessel and said pump to form a closed loop pathway; and operating saidpump so as to mix said sample and said diluent liquid by circulatingsaid sample and said diluent liquid in said closed loop pathway.
 4. Amethod in accordance with claim 3, wherein said reaction solutionflowing from said reactor is maintained at said elevated temperature byheating an enclosure containing said first and second vessels, saidsample conduit and said first, second and third pairs of three-wayvalves.
 5. A method in accordance with claim 4 wherein a vent conduithaving a first two-way valve operably located therein, and a steamsupply conduit having a second two-way valve operably located therein,are connected to said first vessel, said method additionallycomprising:connecting a programmable controller for operating saidfirst, second and third pair of three-way valves, said first and secondtwo-way valve, said block valve and said pump, said programmablecontroller being programmed to automatically operate said valves andpump in the following sequence: a) close said first two-way valve andopen said second two-way valve to admit steam into said first vessel; b)place said first pair of three-way valves in said second position andopen said block valve so as to backflush a flushed solution from saidfirst vessel and said sample conduit into said reactor; c) hold theposition of said block valve, first and second two-way valves and firstpair of three-way valves set froth in paragraphs of a) and b) for alength of time sufficient to flush any reaction solution in said firstcylinder and said sample conduit into said reactor; d) close said secondtwo-way valve and said block valve and open said first two-way valve tovent said first vessel to atmosphere; e) open said block valve and thendelay for about 10 seconds and close said first two-way valve; f) waituntil the pressure in said first vessel is substantially equal to thepressure in said reactor; g) after step f), close said block valve andplace said first, second and third pair of three-way valves in saidfirst position; and h) operate said pump to mix said sample and diluentfluid.
 6. A method in accordance with claim 4, wherein said reactorsolution comprises sodium sulfide as a major component and sodiumhydrosulfide as a minor component.
 7. A method for determining excess ofa minor component in a sample comprising a sodium sulfide reactionsolution containing a minor component of sodium hydrosulfide whichdissolves only at an elevated temperature, wherein the determination isbased on two end point pH titrations, said method comprising thefollowing steps:a) venting a first vessel to atmospheric pressure; b)after step a), establishing flow of said reaction solution to beanalyzed from an elevated pressure in a reactor and directing flow ofsaid reaction solution through a sample conduit having a pre-determinedvolume, and then into said first vessel while maintaining said reactionsolution at said elevated temperature; c) after step b), sealing offsaid first vessel from atmospheric pressure; d) allowing flow of saidreaction solution to accumulate in said first vessel until the pressurein said first vessel substantially equals the pressure in said reactor,thereby assuring that said sample conduit is full of said reactionsolution when flow stops, wherein the volume of reaction solution insaid sample conduit provides said sample of reaction solution; e)diluting said sample of said reaction solution at said elevatedtemperature by mixing with a predetermined volume of liquid diluentcontained in a second vessel to provide a diluted sample; f) coolingsaid diluted sample to about ambient temperature; g) titrating saiddiluted sample to obtain said two end point pH titration of sodiumsulfide and sodium hydrosulfide, wherein a greater quantity of acidreagent added for extinction of sodium hydrosulfide than for sodiumsulfide indicates excess of sodium hydrosulfide; and h) backflushingsaid reaction solution in said first vessel and said sample conduit tosaid reactor.